UiO66-NH2-TiO2/NiF photoanode for photocatalytic fuel cell by towards simultaneous treatment of antibiotic wastewater and electricity generation

Environmental destruction, water crisis, and clean energy are among the very important challenges worldwide based on sustainable development goals. Photocatalytic fuel cell, a potential candidate for converting chemical energy into electrical energy through a pollution-free method, holds promise in addressing these challenges. In this regard, we investigated the response of a photoanode covered with UiO66-NH2-TiO2/NiF on a porous nickel foam as an attractive electrochemical response to remove antibiotics from aqueous solution and simultaneously produce electricity using a one-step hydrothermal synthesis. Nickel foam with its fine structure provides a suitable space for the interaction of light, catalyst, and efficient mass transfer of reactive molecules. It appears that it can be used as a competitive electrode in fuel cells. In order to investigate the properties of the photocatalyst, structural analyses including XRD, FESEM, FTIR, and UV–vis DRS were utilized. Additionally, polarization and electrochemical tests such as chronoamperometry and EIS were measured to further examine the electrochemical features of the PFC photoanode system. The obtained results under optimal conditions (SMZ concentration = 20 ppm, pH = 6, irradiation time = 120 min) were as follows: removal efficiency of 91.7%, Pmax = 16.98 μW/cm2, Jsc = 96.75 μA/cm2, Voc = 644 mV. The light-induced current flow in UiO66-NH2-TiO2/NiF exhibited prominent and reproducible photocurrent responses, indicating efficient and stable charge separation in TiO2/NiF composite materials, which is a promising strategy for pollutant removal and simultaneous electricity generation.


Set-up of photoanode
Set-up of TiO 2 /NiF photoanode The nickel foam was cut into 2 × 3 cm dimensions and then cleaned in acetone, ethanol, hydrochloride solution, deionized water (DI) respectively for 20 min.and then dried in vacuum at 60 °C for 1 h.To prepare TiO 2 /NiF, tetrabutyl titanate was used as a source of titanium.First, Ni foam was immersed in a specific volume/volume ratio of ethanol and tetrabutyl titanate for 20 min and then calcined at 450 °C for 2 h.Finally, 20 ml of tetrabutyl titanate, 25 ml of ethanol, 1 ml of hydrofluoric acid were mixed and stirred for 60 min 40 .After that, the Ni foam and mixed precursor were transferred to a 100 mL Teflon-lined stainless steel autoclave, then heated to 160 °C and kept for 12 h.After natural cooling at room temperature, the prepared samples were thoroughly washed with deionized water and ethanol and then dried at 60 °C for 12 h.Finally, the prepared samples were calcined in a furnace at 550 °C for 2 h to obtain TiO 2 /NiF.
Set-up of UiO-66-NH 2 -TiO 2 /NiF photoanode UiO-66-NH 2 -TiO 2 : UiO-66-NH 2 was synthesized using the same procedure as described in the previous study, with some modifications incorporated 41 .Dissolve ZrCl 4 , 0.2332 gr in 50 ml of DMF, then add acetic acid (6 ml) dropwise to the solution, and finally add 0.1812 gr of BDC-NH 2 to the desired solution and stir for 1 h.The desired mixed precursor was transferred to a 100 ml Teflon-lined stainless steel autoclave, then heated to 120 °C in an oven for 24 h.After naturally cooling, the sample was subjected to centrifugation and washed multiple times with anhydrous methanol to remove any remaining DMF.The resulting pale yellow solid was then vacuum dried at 100 °C for 12 h.
UiO-66-NH 2 /TiO 2 (20% w): In order to create a uniform suspension, a specific quantity of tetrabutyl titanate was dispersed in 100 mL of methanol by stirring for 30 min.Subsequently, an adequate amount of the prepared UiO-66-NH 2 sample (20% weight ratio) was added to the solution while continuously stirring.
UiO-66-NH 2 -TiO 2 /NiF photoanode: The synthesis of UiO-66-NH 2 -TiO 2 /NiF was coated on the nickel foam surface by one-step hydrothermal method.Now the two solutions of MOF and titanium are mixed and stirred for 1 h.After that, the nickel foam and the desired mixed precursor were transferred to a 100 ml Teflon-lined stainless steel autoclave, then heated to 120 °C in an oven for 24 h.After natural cooling at room temperature, the prepared Ni Foams were thoroughly washed with deionized water and then dried at 60 °C for 12 h.Finally, the prepared samples were calcined in a furnace at 450 °C for 4 h to obtain UiO-66-NH 2 -TiO 2 /NiF.It is noteworthy that in order to achieve the appropriate thickness of the catalyst, this process was repeated three times to maintain the amount of the desired catalyst at 10 mg/cm 2 .

Set-up of Cu 2 O/CuO/Cu photocathode
A copper sheet measuring 2 × 3 cm is treated with purified ethanol and then immersed in an aqueous solution containing 2.5 mg of sodium hydroxide and 0.125 mg of sodium persulfate for 30 min.The Cu foil is then dried in an oven at 90 °C for 24 h and Cu 2 O/CuO/Cu is achieved through a process of calcination at 450 °C for 2 h 38 .

Characterization methods
The immobilized photocatalyst is recognized in the following manner: the field-emission scanning electron microscopy (FESEM) with FE-SEM ZEISS Sigma 300, energy dispersive X-ray (EDX), Fourier transform infrared (FTIR) spectroscopy with FTIR Thermo Avatar, the X-ray diffraction (XRD) via Philips PW1730, and, UV-vis diffuse reflectance spectra via (UV-vis DRS) by DRS S_4100 SCINCO.

Degradation test in PFC system
Photocatalytic degradation of SMZ is carried out using an immersed anode and cathode within a singular chamber, without the use of an ion-selective membrane, in a batch reactor.To keep the temperature constant at 25 ± 2 °C, the reactor chamber is cooled by a fan (Fig. 1).The surface of both the anode and cathode is 3 × 2 cm, and there is a distance of 3 cm between the two electrodes.A 300W xenon lamp was utilized as the light source.The SMZ antibiotic solution is stirred in the dark for a duration of 30 min to determine its absorbance.Subsequently, the stirring process is maintained under light conditions, and 2 ml of the solution is periodically extracted from the PFC system.The concentrations of SMZ were determined using a high-performance liquid chromatography-mass spectrometry (HPLC-MS) equipped with a C18 column (2.1 × 100 mm, 3.5 μm) at a wavelength of 270.The mobile phase consists of (A) methanol and (B) trichloroacetic acid in a ratio of 80:20.The degradation efficiency of SMZ is obtained from the following equation.
The C 0 and C represent the concentration and initial concentration at the specified time, respectively.The impact of the parameters, pollutant concentration (10-40 ppm), pH (3-9), and irradiation time (0-120 min) are evaluated.
The quantification of mineralization was assessed using a total organic carbon (TOC, Multi N/C, 3100, Germany) analyzer.

Electrochemical tests
The PFC system utilizes a digital multimeter (specifically, the Victor-VC97 model) to measure voltage and current.The polarization curve is then plotted using the calculated data.Equation ( 2) is used to determine the generated power per unit of anode area.Additionally, the fill factor (FF), an important factor for energy conversion efficiency, can be calculated using Eq. ( 3).
In the equation, P max denotes the real maximum power, J sc corresponds to the short circuit current density, and V oc represents the open circuit voltage 42 .
Photoelectrochemical measurements were performed on using a 25 mL three-electrode test system on an electrochemical workstation, consisting of a working electrode, counter electrode (platinum plate), and reference electrode (Ag/AgCl).TiO 2 /NiF, UiO-66-NH 2 -TiO 2 /NiF and pre-modified NiF were respectively used as working electrodes to determine the electrochemical characteristics.The photocurrent responses of the sample were assessed by measuring the amperometric curve (I-t) with a bias voltage of 0 V (open circuit voltage) for 400 s in Na 2 SO 4 0.5 mol/L electrolyte.Additionally, electrochemical impedance spectroscopy (EIS) was conducted on the synthesized materials in same condition electrolyte, at the open circuit potential within a frequency range of 0.1 to 100 kHz, both in the presence and absence of light.
The surface morphology, size and distribution of Uio-66-NH2-TiO 2 catalyst on nickel foam were characterized by Fe-SEM technique.As depicted in Fig. 3a, UiO-66-NH 2 shows a sleek and symmetrical octahedral morphology with sharp edges.The average side size is approximately 50 nm, which is completely agglomerated with TiO 2 with spherical structure (Agglomerate ball structure) is completely covered (Fig. 3b), which provides more active sites for radiation and contaminant contact.The accumulation of titanium catalyst nanoparticles is attributed to their high surface-to-volume ratio.The provided information indicates that the nanoparticles exhibit a spherical and nearly uniform shape, with an estimated size of approximately 25 nm.Mansouri et al. also obtained similar results in their study with nanoparticles size of approximately 28 nm and showed the stabilization of titania particles uniformly on the synthesized MOF as a support 45 .Figure 3c Fe-SEM shows the successful immobilization of UiO-66-NH 2 /TiO 2 photocatalyst on nickel foam.The crystals have an approximate crystal size in the range of 41-60 nm. Figure 3d and e shows a cross-sectional view of Uio-66-NH 2 -TiO 2 /Ni Foam, it can be concluded that after coating, the hollow structure in the nickel foam is significantly filled.The unique www.nature.com/scientificreports/microstructure topography and interconnected cell structure of nickel foam contribute to a notably expansive surface area.This characteristic aids in effectively immobilizing the catalyst within the foam nickel, rendering it versatile for various applications.Visual examination reveals an uneven surface on the catalyst sheet, presumed to optimize light reflection and enhance its potential for multiple light-utilizing functions.Furthermore, the presence of numerous gaps between the catalyst and nickel foam is anticipated to facilitate efficient transfer, absorption, and subsequent reaction processes 36,37 .Also, the visualization spectrum of elements is shown in Fig. 3g-l.Figure 4 illustrates the FT-IR outcomes of UiO-66-NH 2 /TiO 2 .Bands ~ 575 and 620 cm −1 indicate tensile vibrations of Ti-O 46 .The peak observed at 1044 cm −1 can also be attributed to the existence of carboxylate groups (COO−) within the organic linkages of MOFs 47 .The confirmation of the amine group's presence in the MOF structure is indicated by the sharp stretching vibrations observed at 16,281 cm −1 , which correspond to the N-H bond of the primary amine 48 .The frequency bands at 3421, 2791, and 2857 corresponded to the bending vibrations of O-H and C-H bonds 44 .The OH bond in water molecules can also be identified by the 3421 cm −1 band, which corresponds to its stretching vibrations.Aromatic bands (C=C) can be observed at 2328 cm −1 .The stretching of the C-N band at 1133 cm −1 is also evident for the 2-aminoterephthalate ligand.UiO-66-NH 2 exhibits other characteristic vibrations such as the C-O band at 1044 cm −1 and the out-of-plane N-H motion at 861 cm −148-50 .
To assess the optical response range and explore the interaction between the two components in the catalyst material, a UV-visible emission reflectance spectrum (DRS) was employed.According to the information obtained, the estimated band gaps (Fig. 5) for UiO-66-NH 2 and TiO 2 /Ni nanoparticles are approximately 2.65 eV, 3.21 eV respectively.The UiO-66-NH 2 /TiO 2 composite exhibited the expected inheritance of the optical property from UiO-66-NH 2 .This was evident as the band gap of the UiO-66-NH 2 /TiO 2 , (2.69 eV) nanocomposite was lower compared to that of TiO 2 alone, resulting in an enhanced optical response that extended into the visible region 43 .Additionally, this improvement in optical response helped to prevent electron-hole recombination, thereby enhancing the photocatalytic performance 44 .

Chronoamperometry
The Fig. 6a displays the I-t curves for the electrodes under investigation, indicating the extent of charge transfer during periodic light on/off cycles when the potential was adjusted to 0 V relative to the Ag/AgCl electrode.Pure NiF has minimal impact on light response, but the inclusion of TiO 2 in NiF exhibits a significant effect.UiO-66-NH 2 -TiO 2 /NiF composites demonstrate notable and consistent photocurrent responses, suggesting efficient charge separation within the composite materials containing TiO 2 /NiF.This could be attributed to the enhanced electrical conductivity of nickel foam resulting from the reduced resistance following the deposition of MOF nanoparticles 36 .As a result, UiO-66-NH 2 -TiO 2 /NiF exhibits a rapid and stable optical current generation of 6 μA/cm 2 , whereas NiF only achieves approximately 0 μA/cm 2 in terms of optical current generation.Furthermore, extending the reaction time beyond 400 s did not suppress the intensity of the light current, suggesting that they enhance consistent photoelectric activity.The enhanced conversion of photoelectrons can be attributed to the improved segregation of photo-excited electrons and holes, which can potentially be ascribed to the well-matched band structure and high conductivity of nickel foam.The employment of Ni as a dopant results in a reduction in the band gap.At the same time, the porous characteristics of the photocatalyst trap light effectively and provide a significant contact surface area 35,51,52 .efficiency of electron-hole recombination.In EIS measurements, the electron transfer resistance (R ct ), also known as charge transfer resistance, can be analyzed using Nyquist diagrams.This resistance is represented by the diameter of a semicircle in the diagram.A smaller arc radius in EIS indicates lower resistance to charge transfer and less inhibition of recombination 53,54 .As shown in Fig. 6b, the amount of R ct is shown for UiO-66-NH 2 -TiO 2 /NiF and TiO 2 /NiF.The equivalent circuit model fitted to the impedance data that its components are Ret, the resistance of the electron transfer between the solution and the electrode surface; Z W , the Warburg element; CPE, the constant phase element, and Rs, the solution resistance (Fig. 6c).In the case of UiO-66-NH 2 -TiO 2 /NiF, the smallest observed arc radius corresponds to a reduced resistance against charge transfer.This observation suggests that the deposition of the nanocatalyst has resulted in a decrease in transfer resistance 55 .UiO-66-NH 2 -TiO 2 /NiF can greatly enhance the separation and transfer of electron-hole (e − /h + ) pairs, thereby increasing photocatalytic activity.In the PFC system, the UiO-66-NH 2 -TiO 2 /NiF photoanode, supported by a porous nickel foam substrate, plays a crucial role in generating photo-excited electron-hole pairs and enhancing electrical energy output 37,56 .The impact of process parameters on SMZ degradation in the PFC system The impact of SMZ concentration As illustrated in Fig. 7a, increasing the concentration of SMZ from 10 to 20 resulted in an increase in efficiency from 69.2 to 91.7%.However, when the concentration was further raised 40 ppm, the efficiency decreased to 47.1%.
When the antibiotic concentration is low (10 ppm), the byproducts generated alongside the pollutant compete for the active groups involved in the degradation process, leading to a decrease in the removal rate 13,57 .In general, the formation of hydroxyl radicals is the rate-determining step in the reaction for pollutant removal.This is because hydroxyl radicals react rapidly with pollutants.OH radicals are generated through the reaction of holes with OH − and adsorbed H 2 O.However, if the adsorbed OH positions are occupied by contaminant ions, the production of OH radical's decreases.As a result, the presence of pollutants and their oxidation intermediates negatively impacts the efficiency of pollutant removal by covering the active sites of the photocatalyst 58 .
Figure 7b shows the photocatalytic degradation under different concentrations of SMZ using first order kinetic model.The reduction in removal efficiency and K value at high concentrations (30 and 40 ppm) may be attributed to the adsorption of pollutant molecules on the electrode surface and the active surface of the photocatalyst deposited on the nickel foam.This leads to a decrease in active sites and a delay in light penetration, as reported in references 59,60 .
Also, the power density curve (P-I) in the Fig. 7c demonstrates that the maximum power was achieved at a concentration of 20 ppm.As the pollutant concentration increases, the scavenging of generated h + also increases, leading to an increase in the separation of h + /e − and facilitating more electronic transport to the cathode.Consequently, amplifies energy generation.However, the initial concentration surpasses a certain threshold, the SMZ molecules present in the solution reduce the light absorbed by the photocatalyst.Consequently, the photoexcitation of electrons in the photoanode becomes limited, resulting in lower electricity generation compared to the 20 ppm concentration.Moreover, at 40 mg/L, there may be a decrease in the spontaneous of electrons towards the cathode, which can reduce the production of superoxide radicals (% O 2 − ).These radicals are classified as reactive oxygen species (ROS) and possess the ability to efficiently degrade various types of organic compounds 61,62 .

The impact of pH
The pH of the initial solution plays a crucial role in determining catalyst surface charge factors (active sites) and the properties of organic pollutants.The impact of pH was examined within the pH range of 3.0 to 9.0, by adjusting with 1M HCl and/or NaOH.In different pH conditions, sulfonamides have cationic, zwitterionic and anionic forms 63 .Based on the pK a values, SMZ exists predominantly in positively and negatively charged forms at pH values lower than pK a1 and above pK a2 , respectively.However, between pK a1 and pK a2 , SMZ is primarily present in its neutral form.Since the catalyst has less impact on cationic and anionic species, the highest efficiency was achieved at pH 6 64 .
The UiO-66-NH 2 surface in the pH acidic exhibited a positive charge as a result of the protonation of the amino group.This positive charge led to electrostatic repulsion with cation SMZ ions, thereby resulting in relatively low removal efficiency under acidic conditions.As the pH increases, the amino groups on UiO-66-NH 2 become neutralized 65 .In acidic conditions, there is a higher rate of recombination of electron-hole pairs in the photoanode because of the lower presence of hydroxyl groups in the solution.It is believed that the percentage of hydroxyl groups (% OH) plays a significant role in breaking down the N = N − conjugated system in sulfonamide compounds 66 .At lower pH conditions, a significant number of H + ions have a tendency to interact with the azo bond, thereby decreasing the electron density of the azo group and directly impacting the output power and efficiency of the PFC (Fig. 8a-c).When the pH level was elevated, the catalyst's negative surface repelled the negative charge of SMZ anionic forms and hindered the oxidation of pollutants in the photoanode.Nevertheless, proton reduction can take place in alkaline conditions, leading to the inhibition of the cathodic oxygen reduction reaction (ORR) [67][68][69] .

The impact of irradiation time
Increasing the duration led to an increase in Chances for the photoanode and photocathode to generate a greater number of active radicals and eliminate SMZ 70 .As the reaction time extended from 30 to 90 min, the efficiency exhibited a steep slope and surpassed 85%.With the reaction proceeding for up to 120 min, the efficiency slope became more gradual and reached to 91.7%.

The impact of light intensity
In Fig. 9a-c, the results of radiation intensity changes on the efficiency of pollutant removal (a), simultaneous energy production (b) and kinetic photocatalytic degradation (c) are shown.As it can be seen from the figure, the removal efficiency increased from 42 to 91.7% for the pollutants on average with increasing the radiation intensity from 20 to 100 mW/cm 2 .Increasing the radiation intensity led to the absorption of photons by the anode and the production of more electron holes.On the other hand, the generated electron moves towards the photocathode and superoxide radical is generated, which increases the efficiency.Also, with the increase of light intensity from 20 to 100 mW/cm, the maximum power density of PFC reached from 6.91 µW/cm to 16.98 µW/cm 2 because with the increase of light intensity, the speed of photoelectrochemical reaction in the photoanode increases.With stronger light irradiation, more excited electron-hole pairs were created in the photoanode and the oxidation process of organic substances was strengthened and more electrons were produced and transferred to the cathode.Hence, the performance of the developed PFC increased significantly with increasing light intensity [71][72][73] .

Optimization and performance of PFC system
The optimization is done by the method of one factor in time to find the maximum light degradation efficiency.Under optimal condition ((SMZ concentration = 20 ppm, pH = 6, radiation time = 120), the UiO-66-NH 2 -TiO 2 / NiF composite achieved a performance of 91.7%, while the TiO 2 /NiF composite reached 56% (Fig. 11a).This improvement can be attributed to narrower band gaps and reduced recombination, as indicated by UV-vis DRS analysis.The transfer of electrons from the anode to the cathode can result in an elevation of the superoxide radical within the cathode.Additionally, the excellent electrical conductivity of nickel foam, serving as a substrate, facilitates the efficient separation of hole electrons and reduces recombination.
The analysis of TOC (Fig. 10) under optimal conditions for mineralization resulted in a value of 81.4%, which is lower compared to the SMZ removal value.This decrease may be attributed to the generation of intermediate compounds, necessitating additional time for full mineralization 61 .
The rate constant (k) for a first-order reaction can be determined by using the equation Ln(C 0 /C) = kt.The Fig. 11b shows the degradation kinetics of SMZ during xenon irradiation, which clearly follows a first-order reaction.
To further investigate the photoanode activity, polarization (J-V) and power density (J-P) curves has been drawn (Fig. 11c).The results reveal that the photocurrent response of UiO-66-NH 2 -TiO 2 /Ni is three times higher than that of TiO 2 /Ni.This significant increase can be attributed to the efficient separation and transfer electrons.
In order to assess the efficiency of converting light energy into electrical energy in photocatalytic reactions, the metric utilized is photoelectric conversion efficiency.This is predominantly characterized by two primary criteria: (a) Incident Photon-to-Current Efficiency (IPCE): IPCE gauges the ratio of photocurrent to incident  www.nature.com/scientificreports/photons, offering insights into the effectiveness of electron transport processes during photoabsorption 74 .The calculation is based on formula (4): (b) Chemical-to-Electricity Conversion Efficiency (η): This parameter appraises the overall efficiency of transforming chemical energy generated through photocatalysis into electricity 75 .The calculation is based on formula (5): where λ represents the light wavelength, and P denotes the light power intensity.In optimal conditions, the values for IPCE and η are achieved at 2.611% and 0.177%, respectively.

Reusability and stability of photoanode
One of the influential factors in PFC systems is the stability of the photoanode.The reusability of the UiO66-NH 2 -TiO 2 /NiF anode is assessed for removal efficiency and electrochemistry after five cycles, each lasting 120 min.After 120 min of reaction, the photoelectrodes were withdrawn from the reaction environment and washed with distilled water.The photoelectrodes were dried in an oven at 90 °C and then added to fresh electrolyte for subsequent cycles.The photodegradation of SMZ exhibited a decrease from 91.7 to 88 (approximately 3.7%) after five cycles, which can be attributed to photon corrosion (Fig. 12).
The findings indicated that the catalyst incorporated into the photoanode exhibits favorable photocatalytic properties within the PFC system.Also during the initial cycle, J sc , V oc , and P max were measured at 16.98 μW/ cm 2 , 96.75 μA/cm 2 , and 644 mV, respectively.However, in the fifth cycle, these values slightly declined to 14.92 μW/cm 2 , 92.51 μA/cm 2 , and 600 mV, respectively.This decrease in electrochemical performance can be attributed to the absorption of intermediate products, which subsequently elevate the resistance of the photoanode 76 .Furthermore, the PFC system exhibited a photoanode mass loss rate of approximately 6%, providing further evidence of its long-term stability and excellent recyclability.This indicates that the developed PFC system not only demonstrated high photoelectric activity but also exhibited commendable stability.

Mechanisms
The degradation process of SMZ in the PFC system initiates with the exposure of light to the photocatalyst in both the photoanode and photocathode, resulting in the generation of excited e − and h + at the conduction band (CB) and valence band (VB) edges, respectively (Fig. 13).The photoanode generates holes that can either eliminate pollutants or react with H 2 O to produce OH radicals.These radicals act as powerful oxidizing agents, capable of indiscriminately breaking down organic substances into harmless end products.Excited electrons within the photoanode are transported to the photocathode through the external circuit, thereby minimizing electron-hole recombination.Electrons within the photocathode have the ability to initiate the oxygen reduction reaction (ORR), resulting in the generation of superoxide radicals (O 2 −⋅ ).These superoxide radicals can subsequently undergo reactions with electrons (e − ) and hydrogen ions (H + ) to yield hydrogen peroxide (H 2 O 2 ), as illustrated by the following equations:  In order to clarify the role of UiO-66-NH 2 -TiO 2 /NiF in the charge transfer process, the radical trapping experiment with isopropanol (IPA), ammonium oxalate (OA), benzoquinone (BQ) respectively for OH − , + h, O − 2 radical were used 77 .As shown in Fig. 14, the addition of BQ was less effective in pollutant degradation, while the addition of IPA or OA greatly suppressed the reaction.Therefore, OH and h + radicals may be considered as the main function in pollutant destruction.

Possible pathway of SMZ degradation
Based on the intermediates were identified, possible degradation pathways of SMZ in the PFC system are proposed in Fig. 15.It is assumed that the deamination of the benzene ring in SMZ may result in the generation of P1.The attack of ROS and extraction of hydrogen in -NH 2 might lead to the formation of P 2 .Also, break of the S-N bond (sulfonamide bond) of P 1 /P 2 could produce P 3 .Then, the ring-opening product (P 4 ) could be produced via the cleavage of N-O bond in oxazol ring (P 3 ) 36,78 .

Comparison of SMZ degradation PFC System with some reports
Table. 1 presents some previous reports for comparison about the PFC system.This work employed Cu 2 O/CuO/ Cu mesh photocathode in an easy one-step synthesis, which is cheaper and more accessible compared to many studies that use platinum as cathode.Meanwhile, the use of nickel foam as a support layer with high electrical conductivity and due to its high surface area increases electron transfer and enhances the photocatalytic activity of UiO-66-NH 2 -TiO 2 /NiF as an attractive photoanode with a synthesis of an easy step is used.The commercialization of the PFC system is an important question in this field, which the results of this article can partially answer.

Conclusion
In this study, we used UiO-66-NH 2 -TiO 2 as a photocatalyst for enhancing photocatalytic activity in the visible light region through one-step facile synthesis.The photocatalyst was deposited on a nickel foam substrate, and Cu 2 O/CuO/Cu mesh was utilized as the photocathode.Using nickel foam as a high-conductivity backing layer, and considering its large surface area, enhances electron transfer and strengthens the photocatalytic activity of UiO-66-NH 2 -TiO 2 /NiF.Optimization using a one-factor-at-a-time approach was performed to find the maximum photocatalytic degradation efficiency.Optimization using a one-factor method was performed to find ( the maximum degradation efficiency of light.The process factors have been optimized within the operational range (SMZ concentration = 20 ppm, pH = 6, radiation time = 120).The best performance of the PFC system was achieved under xenon light irradiation for the UiO-66-NH 2 -TiO 2 /NiF and TiO 2 /NiF composites, with efficiencies of 90.4% and 56%, respectively.This can be attributed to shorter band gaps, reduced recombination, and enhanced electron transfer from the anode to the cathode, which can increase the production of superoxide radicals at the cathode.The TOC analysis was 81.4% under optimal conditions for mineralization.Polarization curves (J-V) and power density (J-P) are measured to further investigate the photoanode in the PFC system, which showed that the maximum power in UiO-66-NH 2 -TiO 2 /NiF photoanode compared to TiO 2 /Ni is three times higher, indicating easier electron separation and transfer.The reusability of the UiO-66-NH 2 -TiO 2 /NiF anode with repeatable efficiency for removal and electrochemistry decreased by approximately 3.7% after five cycles (each cycle lasting 120 min).

Figure 1 .
Figure 1.A schematic diagram for experimental set-up.

Figure 10 .
Figure 10.Analysis of total organic carbon (TOC) under optimal conditions.

Figure 13 .
Figure 13.Schematic diagram of reactions occurred during photocatalytic process in PFC system.